Oil pollution

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Oil pollution in Ecuador
Satellite image within the Indian Ocean. Oil films appear as black areas.
Workers clean a coastal area ( Prince William Sound riparian zone)

An oil pollution , the pollution of the environment , particularly the sea , by crude oil or petroleum products . In the case of major pollution, which mainly arises from accidents (in particular from oil tankers ), there is also talk of an oil spill , especially if coasts are also affected (see also list of major oil spills ). Disasters only make a moderate contribution to the overall discharge of oil into the oceans. Probably the largest oil spill to date was a consequence of the Gulf War. However, the world's largest share of oils reaches the sea from land, partly via rivers. In regular ship operation, oils are discharged both legally (see MARPOL ) and illegally. The large proportion that oil tankers caused by washing tanks and taking up ballast water in cargo tanks has declined due to changed regulations and procedures. Oil discharges also occur through natural oil spills, through the entry of volatile hydrocarbons from the atmosphere and through oil production at sea ( offshore ).

Behavior of oil spills in the sea

  • Dispersion: With the exception of a few heavy oils, oil initially floats on the surface of the water. Thin oils (lighter crude oils and most oil products) spread very quickly and form a thin layer that can decrease to monomolecular strength. Viscous oils like heavy oil spread more slowly and form thicker oil slicks . Even crude oil in thin layers ages in a few hours and becomes increasingly tough. The spread by flowing therefore comes to a standstill after a few days at the latest.
  • Evaporation: The volatile components are quickly released into the atmosphere. Gasoline evaporates practically completely within hours, crude oil, depending on the type and temperature, between a third and half within days, with the density approaching that of water. An explosive atmosphere can form over the oil. With heavy oils, the proportion of evaporation drops to 5% and less. Evaporation makes the main contribution to aging.
  • Solution: Volatile components also dissolve in water. This applies in particular to the low molecular weight aromatics , which are essentially responsible for the toxicity of the oils.
  • Drifting: From the moment it is released, the oil drifts due to wind and currents. The division by the swell means that the area affected continues to increase.
  • Dispersion : When there is sufficient wind, the swell breaks thin oil into drops, and tough oil into larger lumps. While the larger ones stay directly on or below the surface and flow together again in the thin liquid case, droplets below a certain size remain stable in the water and are slowly distributed into deeper water layers, over time also to a greater distance. Changing tidal currents have a supportive effect. The concentrations decrease rapidly during this process. The polluted volume of water continues to spread along large currents. This emulsification process is known as dispersion . It also comes to a standstill with increasing age.
  • Emulsification : Water droplets are also introduced into the thin oil on the surface by the swell. In addition to the light raffinates, a creamy water-in-oil emulsion can form here, the water content of which increases to around 70%, becomes increasingly tough and then remains stable ( chocolate mousse ) . It can be foamed by trapped air. In connection with oil contamination, only this process is referred to as emulsification and the product is referred to as emulsion , in contrast to dispersion.
  • Sedimentation: If the dispersion occurs together with solids suspended in the water, e.g. B. swirled sediment or sediment load from rivers, the oil is preferentially deposited on the solids and later sinks with them, which can lead to high oil concentrations on the seabed. Likewise, heavy oil and undispersed crude oil including emulsion ultimately become denser than water through aging and sink in lumps of tar of different sizes . Due to their low interaction with the environment and their dimensional stability, these pose a relatively low risk.
Generalized assessment of the sensitivity of ecosystems to oil pollution
sensitivity Ecosystems
high Mangrove forests
Coral reefs
Salt marshes
protected mudflats
Accumulations of sea birds , marine mammals
(including polar bears) and sea turtles
medium high protected rocky coasts
exposed seagrass mudflats
Estuaries
arctic / sub-arctic ice
medium Pebble beaches
Sea beds on protected coasts
low-medium Sandy beaches
exposed tidal areas
Seabeds on exposed coasts
low exposed rocky coasts
open coastal waters
(protected / exposed refers to the effects of swell and surf)
  • Biodegradation: Oil is broken down at the oil / water interface by certain bacteria ( hydrocarbonoclasts ) found everywhere in the sea . Dispersed oil is readily available to these bacteria because of its large surface area and is therefore quickly broken down. Massive impurities such as chocolate mousse , heavy oil lumps or a layer on the floor are broken down much more slowly. The toxic substances initially bound in the oil with a long biological half-life (e.g. polycyclic aromatic hydrocarbons ) end up in the marine ecosystem during this breakdown; in contrast, low-molecular aromatics in particular are quickly broken down. In some cases, however, additional toxic metabolic products are also produced. The rate of degradation depends on the temperature: At 20 ° C, the rate of degradation is four times as fast as at 0 ° C. Very high molecular weight components of the oil ( asphaltenes ), approx. 5% to 10% in the case of crude oil, are not biodegraded.
  • Oiling of marine animals: In a closed layer, the floating oil dampens the swell, which is why the smoother surfaces are clearly visible from the air and on satellite images (see right picture). As a seeming resting place, these areas attract sea ​​birds . The viscous oil sticks together the plumage, destroys the heat insulation and, in some cases, the swimming ability of the animals and is absorbed by the birds when they attempt to clean it. This usually leads to mass seabird deaths from suffocation, hypothermia, drowning, and poisoning. Other animals that prefer to stay on the surface of the water are also endangered, especially mammals. They also do not perceive recognizable oil as a danger. In contrast, animals in the water column are relatively little endangered.
  • Oiling of coasts: If the floating oil reaches the coast, it first settles there because of the better wetting . Over time, it is washed off by the sea, especially on coasts exposed to surf. Relatively fresh deposits can be relocated several times with changing weather and tide conditions. Lumps of tar that are no longer sticky behave like other flotsam. Still relatively liquid oil or emulsion deposited on beaches suffocates through the closed layer of soil organisms in the affected areas. However, the toxic components can also seriously damage the affected ecosystem in other cases , especially when large quantities of oil are left for a long time, despite weathering. The endangerment of the coasts is particularly great because it is a limited habitat that is practically completely affected.

activities

Combat

Most of the methods of control cause a partial shift in the hazards, so that the choice of means usually requires a weighing up. At sea, in particular with limited pollution, non-intervention is often the most sensible measure, since here the natural processes quickly ensure dispersion and degradation. Even on beaches, an intervention can only worsen the situation. However, it is usually advisable to intervene in the event of major contamination.

At sea

There are several methods of containing oil spills in open water.

Containment with locks
Floating oil barriers laid around New Harbor Island by the US Navy

By oil booms that can be high for the offshore use of several meters, the spread may be an oil slick small area can be prevented. Towing the barrier with two vehicles can push thin oil slicks together, but the speed is limited to less than 1 knot. The containment requires additional measures to remove the oil from the surface. The methods described are impractical in rough seas and promise to contain only 35% of the damage even in calm seas.

Skimming

Oil floating on the surface of the water can be used by special ships (e.g. folding ships like the Bottsand class or the THOR , conventionally constructed ships with outriggers like the Neuwerk or Mellum , catamarans like the Westensee or mixed constructions with a catamaran foredeck like the Knechtsand or MPOSS ). The actual pick-up devices are based on the principle of a weir over which the oil layer flows or on rotating rollers or brushes with scrapers that absorb oil . The still water-containing oil is pumped out of a sump filled in this way and fed into separators, where most of the water is separated off. Different pump systems are sometimes used for low and high oil viscosities. The ships' equipment also includes heated tanks. The efficiency of the current systems begins to decrease at a wave height of 1 meter, from 2 meters upwards it no longer makes sense. This means that it can be used up to approx. Wind force 4. The operating speed is also limited to 1 to 2 knots. The catchment widths for the larger ships are up to approx. 40 meters. In Europe, most countries consider skimming to be the first choice.

Chemical dispersion
A C-130 Hercules distributing dispersants over the Gulf of Mexico

The use of dispersants accelerates the natural dispersion of the oil in the water column and at the same time prevents adhesion to suspended solids. With and in addition to the degradation that takes place in the dispersed oil, more pollutants from the oil are also absorbed by marine organisms. For chemical dispersants to be effective, a minimum value for the swell is required; in heavy swell their use is no longer sensible due to the naturally accelerated dispersion. The Netherlands, for example, has explicitly restricted the area of ​​application to wind speeds of 3 to 7. Further application limits are too high a viscosity of the oil or emulsion formation, which prevents mixing with the dispersant. However, emulsions can be split in an additional operation using demulsifiers . Also shallow water depths, usually 20 meters, are set as the limit, which would lead to high oil concentrations in the water column, and the lack of exchange currents in some coastal areas limit the use. Due to these conditions, this method is preferably used in Europe in the Atlantic. The dispersant must be precisely dosed and applied specifically to the oil slick, which requires the carpet's layer thickness to be determined. It must be used within a few hours before the oil ages too much or emulsifies. The most important resource is therefore the aircraft, but it is also possible to deploy helicopters or ships. Great Britain has two spray planes.


Oil Dissolver

Since 2015 there have been biological oil dissolvers, which break down crude oil or machine oil into its original constituents hydrogen, oxygen and nitrogen.

These funds pose no threats to flora and fauna. The biological processes are extremely accelerated by concentrated enzymatic components. Another advantage is that it can be applied using conventional spray systems. The oil dissolvers can also be used for ballast water treatment via dosing systems.

combustion

Controlled combustion requires a minimum layer thickness of between 2 mm for fresh crude oil and 10 mm for heavy oil and emulsified oil, which may also contain a maximum of 30% water. Special fireproof barriers can be used. In addition to other pollutants, 10 to 14 percent of the amount of oil converted ends up in the air as only partially burned particles. Further combustion residues sink and can endanger the seabed ecosystem . In Europe u. a. refrained from using this method due to unfavorable geographical conditions. The method came u. a. for use in the case of the Exxon Valdez .

Bioremediation

If the natural bacterial breakdown of oil spills is limited by the supply of nutrients, which can be the case for phosphates and nitrates on the high seas, these nutrients can be added. However, the practical scope of this procedure is very limited by the requirements. The genetic engineering performance improvement of bacteria that break down hydrocarbons is the subject of research, since certain groups of substances are broken down very slowly by the bacteria present. Due to the problematic impact assessment of a release of such modified organisms, their use is not foreseeable.

At the beach

If the oil reaches the coast, it will immediately poison or asphyxiate soil organisms (such as worms) in the affected areas. Cleaning up the beaches only allows repopulation here. Improper cleaning attempts can also get oil into deeper layers of sand, where it is no longer broken down.

Treatment of animals

Washing oily birds is very controversial as very few birds can actually be released back into the wild. Birds that have already poisoned themselves through ingestion of oil do not have a high chance of survival even after being cleaned.

To protect little penguins on the south coast of Australia after an oil spill, penguin sweaters are knitted around the world :

“Most of the animals make it on land in such cases, but are then too weak for the time-consuming cleaning procedure. Wrapped up warm, you can relax first. In addition, the knitting stitches prevent the animals from pecking the poisonous matter out of their plumage with their beak and swallowing it. "

The penguin sweaters have already proven themselves after the wreck of the freighter Rena (New Zealand). Almost all of the 400 oil-smeared penguins were released back into the wild in good health.

Prevention

The prevention of oil pollution of the seas is the enforcement of agreements for transport and mining. It must be possible to tow tankers in distress at sea. For this it is necessary to have strong rescue ships ready.

The flight control of busy marine areas and the introduction of double-walled tankers are part of the prevention. Double-walled tankers offer more safety in the event of a collision or run aground. Furthermore, ballast water can be taken up in the double-walled space instead of in the tanks, so that oil residues do not lead to water pollution.

The radar monitoring of the routes and the adequate qualification of the crew of the large, difficult-to-maneuver tankers play a role in preventing accidents.

Most oil production platforms have separate safety valves on the seabed ( blowout preventer ), which close the production pipe in the event of an accident on the platform. These platform safety devices can prevent an oil spill. A possible failure of these valves became known in late April 2010 and in the following months, when the Deepwater Horizon drilling platform in the Gulf of Mexico sank after an explosion and it was initially impossible to stop the oil pouring out.

International agreements

See also

Web links

Commons : Oil Spill  Album with Pictures, Videos and Audio Files

Individual evidence

  1. ^ The greatest oil spill of all time, The greatest oil spill of all time, michaelsimm.de, February 2, 1991
  2. ↑ according to the Impact Reference System of the Community Information System for the Control and Reduction of Pollution of the European Commission.
  3. ↑ merkur-online.de: Why the penguins in Australia wear sweaters. March 17, 2012, accessed August 31, 2012 . (Knitting instructions here ; PDF; 185 kB).
  4. ^ Bonn Convention